A series of synthetic iron porphyrins are being prepared for the purpose of modelling the oxygen binding hemoproteins--hemoglobin, myoglobin, and cytochrome P-450. The structures of these synthetic models are being determined by X-ray diffraction and their physical properties (Mossbauer, electronic, and MCD spectra, magnetic moments, and vibrational spectra) are being determined for comparison with the natural hemoproteins. Special emphasis is being given to studies of models for the hydroxylase cytochrome P-450. Electrochemical experiments directed towards mimicking hydroxylase activity are in progress. To date, synthetic models for oxymyoglobin, deoxymyoglobin, and three states of cytochrome P-450 have been characterized. The vibrational frequency for coordinated dioxygen has been measured in both iron and cobalt porphyrin complexes.